SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21b43281582c10bcd17ade6871c076b132564e617b5a841d38b983772f4a9c70' 
  AND token = '+4dqH4pZ4CIsRNGuiAVjv1hN/bEFCn6PRkTRsJMupQY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00049

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}